Wastewater remediation is a broadly studied art with many innovations. Waste is treated aerobically, anaerobically or both. In waste water, especially from industrial waste, there is an accumulation of biomass, called biosolids or sludge. It is costly and difficult to treat biosolids because the contents are virtually unknown and unknowable. Therefore, much of the biosolids are concentrated, digested, composted, land applied or entombed in landfills and the like.
Aerobic systems for treating waste products, including sludge, are well known. They usually involve oxygen-addition, return activated sludge (RAS) as a source of active aerobic bacteria, a mixing step and a clarification step. Some of the clarified solids are returned as RAS or are wasted (WAS).
Anaerobic systems for treating waste products, including sludge, are also well known. A common reactor design is the Up-flow Anaerobic Sludge Bed (UASB). Wastewater is pumped into a granular sludge bed to fluidize the granules. Fluid flow allows the gas to escape and the granules return to the fluidized bed. The granules self-form or can be introduced from an outside source.
The biochemistry of biofilms on minerals is well known. A solid mineral is formed (or introduced as a seed crystal). Bacteria colonize onto the surface of these seed crystals. The first colonizers die as they make a sacrificial glue to bind the biofilm to the surface. More colonizers form a synergistic organized collection of bacteria. Bacteria secrete a biopolymer that can bind small mineral crystals to the surface, building up a granule.
Attached growth surfaces are well known. In creeks, for example, slime grows on rocks as flooded aerated water flows by generally in one direction (downhill). In trickling filters, wastewater trickles down over rocks while air is bubbled up from below. Trickling filters are not flooded. An entire ecosystem grows in the thin, aerated film that grazes on the dead and dying attached bacteria. The grazing keeps the trickling filter from fouling.
More recently Kania et al., U.S. Pat. No. 8,372,277 (Kania '277), disclosed a floating streambed of a permeable matrix flooded by flow from a circulator, with or without added air and intended to de-stratify the water column. Kania '277 teaches flow through the permeable matrix. However, a periphyton layer grows over the surface, requiring periodic cleaning.
Circulators are well known (Roberts et al., U.S. Pat. Nos. 8,298,411 and 7,329,351). Impingement aeration to make fine bubbles is also known (Bettle U.S. Pat. No. 5,772,886). The contents of the art cited in this paragraph are incorporated by reference.
Other circulators are described in PCT Publication No. WO 2014/176388, the contents of which are incorporated by reference.
Granules are common in up-flow anaerobic reactors but are not common in ponds as there are no seeds to start the process. The present disclosure provides a means of generating these granules in a controlled location in a higher concentration and as a result, provides a more effective method for removing the sludge in the waste water.
Other investigators have found that calcium level affects granule formation. For example, intermediate levels of calcium form granules that reduce COD faster. However, additional calcium cements in the granules and reduces COD removal.
Still other investigators have suggested that the definition of granules is related to the Sludge Volume Index (SVI), a standardized test that quantifies the settling rate of wastewater flocs, such as mixed liquor suspended solids (MLSS) and anaerobic granules in a UASB.
More recently, investigators have studied biofilms in wastewater treatment systems. They report that bacteria use quorum sensing (QS) and quorum quenching (QQ) to control biofilm development. The subject is very complex, but can generally be explained as:                1) Planktonic bacteria colonize a surface        2) Bacteria produce a polymeric glue that attaches bacteria to the surface        3) A structured biofilm is formed on the surface when QS chemicals signal that there are sufficient bacteria available to form the biofilm.        4) QS chemicals signal bacteria to build the biofilm; QQ chemicals signal bacteria to stop building the biofilm. Hence QS encourages biofilm growth; QQ discourages biofilm growth.        5) QS chemicals are affected by pH. At mildly basic pH, the ring structures can be enzymatically opened, reducing QS chemicals. At slightly acidic pH, the ring structures can be reconstituted, increasing QS chemicals. Thus a slight acidification will help build a biofilm. At highly basic or highly acidic conditions, QS chemicals are inactivated. In aerobic systems, biofilms are generally undesirable because they tend to plug the pores in, for example, a membrane bioreactor.        
Granules have to be defined because they vary. Some researchers have defined granules as having a size greater than 100 microns and an SVI of less than 50 mg/l. Others have added the concentration of calcium. But the practical reality is that granules are a subset of an active biofilm. Sometimes granules are structured as gels and not as minerals. This can occur in the same pond over time as ancient (legacy sludge) is digested and formerly entombed calcium is lost in the effluent.
A more comprehensive definition of an anaerobic granule includes:                1) An SVI of less than 50 mg/l (to capture the rapid settling nature of the biofilm).        2) A pH>6.2 and <7.2 (to capture the need to select for QS chemicals).        3) Conductivity greater than 800 Siemens/m (to capture that the active biofilm exists in a high electrolyte brine)        4) Oxidation Reduction Potential (ORP) is more negative than −200 mV (to capture that the granule is an anaerobic granule).        
Another important concept is advection. In physics, engineering, and earth sciences, advection is the transport of a substance. The properties of that substance are carried with it. Most generally the advected substance is a fluid. An example of advection is the transport of pollutants or silt in a river by bulk water flow downstream. When wastewater flows over an active biofilm granule bed, some of the QS and QQ chemicals are carried in the advected fluid. If the advected fluid returns directly to the bed/supernatant interface, then the QS and QQ fluids are not lost.